Restaurant grades are making the city healthier and wealthier, Mayor Bloomberg proclaimed yesterday.

Armed with data gleaned from the 20-month-old cleanliness scoring system for food establishments, the mayor announced that salmonella infections fell to 13.7 per 100,000 — the lowest rate in 22 years — in the program’s first full year of 2011.

In the first nine months since restaurateurs had to start displaying their A, B or C ratings, business jumped 9.3 percent, or $800 million, he added.

Most were more than happy to comply, the mayor explained, since 72 percent now have the top grade.

“It may just be that clean kitchens are as good for business as clean air is when a restaurant is smoke-free,” Bloomberg said from the popular Zero Otto Nove restaurant in The Bronx, which has an A grade.

The once-controversial administration initiative has been copied worldwide.

“Some feared it would drive away customers,” the mayor said of the grades instituted in July 2010. “Well, I’m happy to say exactly the reverse has happened.”

The New York State Restaurant Association had a hard time swallowing that assessment.

“It is misleading and incorrect to insinuate that restaurant sales are up due to the letter-grade system,” said Andrew Rigie, the group’s executive VP. “In fact, even A-letter-grade restaurants are struggling because of the fines and fees associated with the system.”

City Council Speaker Christine Quinn, who is scheduled to hold a hearing today on all inspection protocols, was another skeptic.

“Revenue at restaurants may be up 9.3 percent since grading began, but fines are up 145 percent since 2006,” she said. “We can protect public health without shutting down businesses.”

Bloomberg dismissed the critics out of hand.

“Their complaints are going to fall on deaf ears, I can tell you that,” he said. “We’re not going to change.”

Owners and managers of two restaurants near City Hall — both with A’s in their windows — expressed support for the grading system, but questioned how much extra revenue it pulls in.

“Is it good for business? No. My business has stayed the same,” said Frank Djerdjaj, owner of the Little Italy Pizza shop on Park Place.

“It didn’t get better because I got an A.”

A few blocks and a sizable number of dollars away, manager Scott Young of The Palm Restaurant on Chambers Street credited a revitalized TriBeCa neighborhood for an uptick in customers.

“I wouldn’t say it’s due to the grading system,” he offered.

Unlike some restaurateurs who have lashed out at the system, Young praised the city’s corps of younger inspectors as conscientious and caring.

“It’s much better than it was years ago, when people seemed bored with the job,” he said. “The new people take it seriously.”

In Chinatown, where the streets are among the most congested in town, restaurateurs said the grades counted.

“I have seen more people coming in since I got the A,” said Danny Zou of Thai So’n on Baxter Street. “People care about the letter. They trust us more.”

Cashier Wanling Wong at A-rated Vivi Bubble Tea agreed.

“The business has gotten a lot better since we put the sign in the window,” she said.

“It was always good, but now it is much better. People can see how clean the restaurant is and how good the food is.”